Is Windows Security essentials enough protection for your computer?

The quick answer is No

Microsoft Security Essentials is average in many ways; it's OK but it isn't the best anti-virus software you can get, even for free. I suggest you check out some real world tests that put the anti-virus software through some tough tests and then list the results so you can see which is the 'best' or right one for you. A site like AV Comparatives is good for this.